This invention relates generally to pneumatic tires and more particularly to such a tire having improved lateral beam stiffness of the tread due to the breaker structure therein.
In the manufacture of pneumatic tires, it is known to provide such tires with one or more layers of material between the carcass and the tread to stiffen the tread. Such layers are known generally as breaker plies and will be referred herein as breakers. The breakers themselves may be formed of any suitable reinforcing material held in place by an elastomer.
The purpose of the respective breakers is to stiffen the tread such that a more uniform "footprint" is presented between the tire and the ground. The breakers also provide more rigidity in the horizontal plane of the footprint. While all the factors contributing to "squirm" are not known, it is known that squirm of the tread within the footprint seriously decreases tread life and may cause additional heat to be generated within the tire structure. In addition, lateral forces imparted to the tire structure during turning movements will also cause a squirm effect in the footprint. The breakers are a method of construction which tends to lessen the effect of squirm.
In the manufacture of a tire, the breakers are positioned on the carcass so that the principal reinforcing fibers are at an angle with respect to the mid-circumferential plane of the tire band. In the conventional open-center toroidal tire the initial angle will change to some other angle in the completed tire since the flat tire band must "grow" in the press and vulcanizing mold to its final open-center toroidal shape. While the breaker reinforcing fibers or the like may be parallel when applied to the tire band, as the band is formed into the conventional tire shape, such parallel fibers will pantograph due to the tire molding process.
It has also been noted that tires having been manufactured with various plies or breakers inherently have a degree of "ply steer". Ply steer is the tendency of the tire to steer in the direction of the last applied bias belt. The amount of ply steer depends on the reinforcing material used in the ply as well as the angle at which the ply is applied to the tire relative the mid-circumferential plane.
Breaker plies heretofore in use have been substantial in weight and construction. The breakers must resist hoop forces from the inflation of the tire as well as centrifugal forces imparted thereto when the tire is in use, often at substantially high speeds.
Accordingly, it is an object of this invention to provide a pneumatic tire having a breaker structure to provide increased stiffness in the tread and rigidity in the horizontal plane of the footprint of the tire during application of turning forces to the tire.
Another object of this invention is to provide a pneumatic tire in which the breaker structure has a uniform placement of the reinforcing material from side to side.
A still further object of this invention is to provide a pneumatic tire having a breaker structure in which the reinforcing fibers of a given direction in the breaker ply are all at substantially the same angle throughout the footprint.
And yet another object of this invention is to provide a pneumatic tire in which ply steer is substantially eliminated through the use of a circumferential belt.
And yet a still further object of this invention is to provide a pneumatic tire having a breaker structure in which the breaker structure can be very light without decreasing the enhanced beam stiffness.